A swat team enters the main gate Thursday at Fort Hood, Texas. A soldier opened fire at a U.S. Army base in Fort Hood, unleashing a stream of gunfire that left 12 people dead and 31 wounded. The incident appears to be the worst mass shooting at a U.S. military base. Officials have not ruled out the possibility that some casualties may have been victims of “friendly fire,” shot by authorities amid the mayhem and confusion at the scene, said a senior U.S. official.